Boring technique using locate point measurements for boring tool depth prediction

ABSTRACT

A method is disclosed as part of an overall process in which a boring tool is moved through the ground within a given region along a particular path in an orientation which includes pitch. A locating signal is transmitted from the boring tool which signal exhibits a field defined forward point within a reference surface which field defined forward point is vertically above an inground forward point on the particular path through which the boring tool is likely to pass. The method establishes a predicted depth of the boring tool at the inground forward point by first identifying the field defined forward point. The signal strength of the locating signal is then measured at the field defined forward point as being representative of the depth of the boring tool at an inground upstream point which is the current location of the boring tool. With the boring tool at the upstream inground point, the pitch of the boring tool is determined. Using the measured signal strength and the determined pitch, the predicted depth of the boring tool is determined for the inground forward point based on the boring tool moving along an approximately straight path to the inground forward point.

RELATED APPLICATIONS

The present application is a continuation application of priorapplication Ser. No. 11/215,540 filed Aug. 30, 2005,now U.S. Pat. No.7,049,820 which is a continuation application of application Ser. No.10/854,855 filed May 27, 2004 and issued on Oct. 11, 2005 as patent U.S.Pat. No. 6,954,073; which is a continuation of application Ser. No.10/389,423 filed Mar. 13, 2003 and issued on Jan. 4, 2005 as patent U.S.Pat. No. 6,838,882; which is a continuation of application Ser. No.10/116,505 filed Apr. 4, 2002 and issued on May 6, 2003 as patent U.S.Pat. No. 6,559,646; which is a continuation of application Ser. No.09/659,908 filed on Sep. 12, 2000 and issued on May 28, 2002 as patentU.S. Pat. No. 6,396,275; which is a continuation of application Ser. No.09/448,647 filed on Nov. 24, 1999 and issued on Dec. 12, 2000 as patentU.S. Pat. No. 6,160,401; which is a continuation of application Ser. No.09/047,874 filed on Mar. 25, 1998 and issued on Jan. 11, 2000 as patentU.S. Pat. No. 6,014,026; which is a continuation-in-part of applicationSer. No. 08/990,498 filed on Dec. 15, 1997 and issued on Aug. 3, 1999 aspatent U.S. Pat. No. 5,933,008; which is a continuation-in-part ofapplication Ser. No. 08/712,325 filed on Sep. 11, 1996 and issued onJun. 9, 1998 as patent U.S. Pat. No. 5,764,062; which is acontinuation-in-part of application Ser. No. 08/615,467 filed on Mar.14, 1996 and issued on Dec. 16, 1997 as patent U.S. Pat. No. 5,698,981,the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to an underground boringtechnique, especially one which is intended to install undergroundutility cables, and more particularly to a specific technique for usinglocate point measurements in predicting the depth of a boring tool at aforward point along a particular path of movement of the boring tool.

Installing underground utility cable using a steerable boring tool iswell known in the art. Various examples are described in continuingMercer U.S. Pat. Nos. 5,155,442, 5,337,002 and 5,444,382 and pendingU.S. application Ser. No. 442,481, filed May 16, 1995 which is acontinuation of Mercer Patent U.S. Pat. No. 5,444,382 (collectivelyreferred to herein as the Mercer Patents), all of which are incorporatedherein by reference. An example of the prior art Mercer technique isbest illustrated in FIG. 1 herein which corresponds to FIG. 2 in theMercer Patents. For purposes of clarity, the reference numerals used inthe Mercer Patents have been retained herein for like components.

As seen in FIG. 1, an overall boring machine 24 is positioned within astarting pit 22 and includes a length of drill pipe 10, the front end ofwhich is connected to the back end of a steerable boring head or tool28. As described in the Mercer Patents, the boring tool includes atransmitter or sonde for emitting a dipole magnetic field 12 whichradiates in front of, behind and around the boring tool, as illustratedin part in FIG. 2. A first operator 20 positioned at the starting pit 22is responsible for operating the boring machine 24, that is, he or shecauses the machine to let out the drill pipe, causing it to push theboring tool forward. At the same time, operator 20 is responsible forsteering the boring tool through the ground. A second locator/monitoroperator 26 is responsible for locating boring tool 28 using a locatoror receiver 36. The boring tool is shown in FIG. 1 being guided aroundan obstacle 30 at a generally constant depth beneath a reference surface32 until it reaches a termination pit 34. The locator/monitor operator26 holds locator 36 and uses it to locate the surface position directlyabove tool head 28. Once operator 26 finds this position, the locator 36is used to determine the depth tool head 28. Using the particularlocator of the present invention, operator 26 can also determine theorientation (yaw, pitch and roll) of tool head 28 and other informationpertinent to the present invention, as will be described hereinafter.This information is passed on to operator 20 who uses it to steer theboring tool to its target.

As stated above, the overall arrangement illustrated in FIG. 1 may beused to install underground utility cable. After the boring tool reachestermination pit 34, the cable is connected to the drill pipe and pulledinto position within the ground as the drill pipe is pulled back throughthe underground tunnel to starting pit 22. Once the utility cable is soinstalled, it would be quite desirable to have a record of where it isactually located within the ground, even if the terrain of the groundchanges with time. As will be seen hereinafter, the present inventionfulfills this desire in an uncomplicated and reliable way using much ofthe technology described in the Mercer Patents.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter, a method is disclosedas part of an overall process in which a boring tool, for example boringtool 28 is moved through the ground within a given region along aparticular path in an orientation which includes pitch. A locatingsignal is transmitted from the boring tool which signal exhibits a fielddefined forward point within a reference surface which field definedforward point is vertically above an inground forward point on theparticular path through which the boring tool is likely to pass. Themethod establishes a predicted depth of the boring tool at the ingroundforward point by first identifying the field defined forward point. Thesignal strength of the locating signal is then measured at the fielddefined forward point as being representative of the depth of the boringtool at an inground upstream point which is the current location of theboring tool. With the boring tool at the upstream inground point, thepitch of the boring tool is determined. Using the measured signalstrength and the determined pitch, the predicted depth of the boringtool is determined for the inground forward point based on the boringtool moving along an approximately straight path to the inground forwardpoint.

DESCRIPTION OF THE DRAWINGS

The particular embodiment of the present invention described brieflyabove and the present invention generally will be described in moredetail hereinafter in conjunction with the drawings wherein:

FIG. 1 is a partially broken away elevational and perspective view of aboring operation described in the previously recited Mercer Patents;

FIG. 2 is a diagrammatic illustration of a boring tool used in theoperation shown in FIG. 1 and particularly depicts, in part, theelectromagnetic radiation pattern emitted from the transmitter containedby the boring tool;

FIG. 3 is a side elevational view of a locator or receiver which may beused in the operation illustrated in FIG. 1 but which has been modifiedin accordance with the present invention;

FIG. 4 diagrammatically illustrates the way in which the boring tool ofFIG. 1 communicates with the locator of FIG. 3 and the way in which thelocator communicates with a cooperating receiver forming part of aremote processing system at the starting pit, that is, at the startingpoint for the boring tool;

FIG. 5 diagrammatically illustrates the way in which the boring toolactually moves through the ground from its starting point to itsterminating or target point along with a particular reference pathbetween those two points;

FIG. 6 diagrammatically illustrates an overall arrangement which isdesigned in accordance with a first embodiment of the present inventionand which utilizes much of the technology of the Mercer Patents and theremote processing system generally shown in FIG. 4 and designed inaccordance with the present invention to carry out a method ofestablishing and recording the actual path taken by the boring tool, asshown in FIG. 5;

FIG. 7 diagrammatically illustrates a particular procedure used in thelast mentioned method;

FIGS. 8A, 8B, & 8C diagrammatically illustrate the way in which thelocator of FIG. 3 is used to determine the position of the boring toolof FIG. 1 when the boring tool is at any given measuring location on itspath of movement shown in FIG. 5 while the locator is positioned at acorresponding reference point on the reference path which is shown inFIG. 5;

FIG. 9 diagrammatically illustrates an overall arrangement which isdesigned in accordance with a second embodiment of the present inventionand which utilizes all of the technology of the arrangement illustratedin FIG. 6 and additional technology in order to carry out the method ofnot only establishing and recording the actual path taken by the boringtool relative to a reference path, but also establishing and recordingthe reference path itself which may subsequently change with time and avertical survey reference level which will remain unchanged with time;

FIG. 10 diagrammatically depicts a way in which the arrangement of FIG.9 establishes the path taken by the boring tool, the reference path, andthe vertical survey reference level recited immediately above;

FIG. 11 graphically depicts the path taken by the boring tool, thereference path and the vertical survey reference level, all of which areestablished and graphically recorded by the arrangement of FIG. 9;

FIGS. 12 and 13 diagrammatically illustrate more detailed positionalrelationships between the boring tool and ground level;

FIGS. 14, 15 and 16 diagrammatically illustrate, in block diagram form,a preferred overall arrangement for carrying out the same function asthe arrangement of FIGS. 6 and 9.

FIG. 17 is a diagrammatic elevational view illustrating the depthprediction method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning again to the drawings, attention is immediately directed to FIG.3 which illustrates a locator 36′. With exceptions to be noted, locator36′ may be identical to locator 36 described in the Mercer Patents.Therefore, the same reference numerals used to describe locator 36 inthe Mercer Patents have been used to designate corresponding componentsin locator 36′. In order to understand and appreciate the presentinvention, the only particular components of locator 36′ that form partof locator 36 and that are important to note here are the antennareceiver arrangement comprised of orthogonal antennae 122 and 124 andassociated processing circuitry for measuring and suitably processingthe field intensity at each antenna and roll/pitch antenna 126 andassociated processing circuitry for measuring the pitch and roll of theboring tool. Note specifically that when the base 127 is horizontal andin the plane of the paper, the orthogonal antennae 122 and 124 extend45° from both the horizontal and vertical. With this in mind, there willbe provided immediately below a brief description of the way in whichlocator 36′ is used to locate boring tool 28.

Returning to FIG. 2, as previously mentioned, the boring tool 28includes a transmitter which emits magnetic field pattern 12. Forpurposes of the present discussion, let it be assumed that the boringtool is located within the ground immediately below point P1 and isoriented horizontally in the plane of the paper so as to display zeropitch and zero yaw and thereby simplify the present example. Under thesecircumstances, the flux field from the pattern comes up through theground with a vertical component within the plane of the boring tool atwhat may be referred to as a front locate point and a similar verticalflux component extends upward through the ground immediately behind andin the same plane as the boring tool through at what may be referred toas a rear locate point. These front and rear locate points are referredto as lateral locates in the Mercer Patents and, herein, as a group theymay be referred to as negative locate points. They can be found bylocator 36′ in the manner described in the Mercer Patent and referenceis made thereto. Briefly, however, operator 26 knows when the locator isdirectly above either the front locate point FLP or the rear locatepoint RLP because these are the only isolated two points in which theflux field from the magnetic field pattern bisects the antennaearrangement 122, 124 in the manner shown by a dotted line at 12 a inFIG. 3. The operator can tell when this occurs because the fieldintensity detected by the two antennae will be equal at these two pointsand the change in relative antenna intensity with movement of thelocator will be different than for the points immediately above theboring tool. Finding these locate points is important to the presentmethod, as will be seen hereinafter. The fact that the two locate pointslie in a plane through the axis of the boring tool is also important tothe present method, as will also been seen.

Referring to FIG. 4, the boring tool 28 is shown in the same horizontalposition as FIG. 2 and immediately above the boring tool is locator 36′.A remote processing system generally designated by the reference numeral500 is shown positioned at starting pit 22. The purpose of this FIG. 4is to illustrate one main difference between locator 36′ and locator 36.The latter is able to receive pitch and roll information from boringtool 28 by means of radio wave but there is no such communicationbetween locator 36 and any receiving equipment at starting pit 22. Incontrast thereto, locator 36′ upon receiving the same information fromthe boring tool includes readily providable means to be described inconjunction with FIG. 6 including a transmitting antenna 504 (see FIGS.4 and 6) for relaying roll and pitch information to cooperating receiverhardware 500 as well as other positional information of the boring toolprocessed by locator 36′. All of this information, that is, the roll andpitch and other positional information is processed by system 500 inaccordance with the present invention, as will be described hereinafter.

Turning now to FIGS. 5-7, attention is directed to the way in whichlocator 36′ is used by operator 26 in cooperation with remote processingsystem 500 and boring machine 24 which is used by operator 20 in orderto establish and record the actual path taken by boring tool 28 as itmoves from its starting point, for example starting pit 22, to itstarget point, for example termination pit 34. FIG. 5 diagrammaticallydepicts the starting point ST, the termination or target point T, theactual path taken by the boring tool, which path is indicated at AP anda reference path RP, all of which are located within a given region 506.For purposes of clarity, region 506 is set within a Cartesian coordinatesystem where the x-axis extends horizontally in the general direction offorward movement of the boring tool, where the y-axis represents thehorizontal, general lateral direction with respect to the boring tooland where the z-axis represents vertical depth. For purposes of thepresent discussion, it will be assumed that the boring tool 28 is causedto move along path AP by operator 20 who momentarily stops the boringtool at various spaced apart measuring locations which are indicated at508 in FIG. 5. These measuring locations may be provided at regularspaced intervals or irregularly spaced intervals and the distancebetween measuring locations may vary. In one embodiment, the distancebetween each measuring location is one drill rod making up drill pipe10, which drill rod is approximately 10 feet. Suitable and readilyprovidable means may be used to actually measure the amount of drillpipe in the ground and report the amount to system 500, as indicated byarrow 501 in FIG. 4. As will become apparent hereinafter, by spacingmeasuring locations close to one another, the actual path AP taken bythe boring tool can be accurately established and recorded. Referencepath RP extends along the surface of the ground and can be the groundlevel component of the intended path taken by the boring tool or it canbe a laterally spaced ground level component, as illustrated in FIG. 5.In either case, it must be established either prior to the actual boringoperation or as the boring operation proceeds, as will become apparent.

With the foregoing in mind, attention is now directed to the way inwhich the boring operation proceeds. At the start, operator 20 drivesthe drill pipe 10 out of machine 24 which, in turn, pushes drill head infront of it. At the same time, the boring tool is guided by operator 20in the intended direction. In order for the boring tool to be guided inthis way, operator 26 follows it with locator 36′. As this operator doesso, the locator 36′ and boring tool 28 cooperate with one another togenerate certain information about the position of the boring toolrelative to the position of the locator. Two specific components of thispositional information are the intensities of electromagnetic field 12at the locator as measured by antennae 122 and 124. The measuringinformation may also include the pitch and roll positions of the boringtool which are measured directly by sensors on the boring tool andtransmitted by means of radio wave from the boring tool to the locator.In the case of the Mercer Patents, this information is processed bylocator 36 and operator 26 using this processed information conveys itverbally to operator 20 who uses it for guiding the boring tool. In thecase of the present invention, while locator 36′ processes theinformation in the same manner as locator 36, the processed informationis relayed from locator 36′ to remote processing system 500 for furtherprocessing by the latter, as previously mentioned in conjunction withFIG. 4. The way in which locator 36 processes this information in orderto determine the position of the boring tool at any given point in timeis described in the Mercer Patents and reference is made thereto. Thisis the case whether the locator is directly over the boring tool asillustrated in FIG. 1 or laterally to one side of the boring tool aswill be seen hereinafter in the case of the present invention.

As boring tool 28 is moved along its actual path AP, the positionalinformation described immediately above is continuously generated andprocessed so that the boring tool may be appropriately guided. However,heretofore this information has not necessarily been recorded in anypermanent form. In the case of the present invention, as will be seen,it is recorded intermittently, specifically at spaced apart measuringlocations 508, and in accordance with a specific, consistent procedurewhile the boring tool is at a momentary standstill at each suchmeasuring location, as will be described immediately below inconjunction with FIG. 7.

Turning to FIG. 7, the boring tool 28 is shown momentarily stopped atits first measuring location 508. With the boring tool in thisstationary position, operator 26 uses locator 36′ to locate one or bothlocate points FLP and RLP in the manner described in the Mercer Patents.In this regard, if as in the present case this is the first measurementand the operator is not sure of the direction of the boring tool, i.e.its yaw direction, he or she might wish to measure both the front locatepoint FLP and the rear locate point RLP in order to establish the axisof the boring tool, which axis extends through the two locate points. Insubsequent measurements, if the operator knows the yaw direction of thestationary boring tool, it may be only necessary to measure one of thelocate points, for example the front locate point, in order to establishthe boring tool's directional axis. As stated previously, the locatepoints, either the front locate point or the rear locate point, isestablished when the vertical component of the electromagnetic field 12bisects antennae 122, 124 when the antennae are above the locate pointand, in the case of region 506, in the x, z plane as illustrated in FIG.8 b. Once the operator finds the appropriate locate point, either facingtowards or away from the boring tool, the rest of the procedure would bethe same one for each measurement. Should the operator select forexample the front locate point, he or she then rotates the locator 90°either to the right or to the left but consistently, for example to theright if the operator is facing away form the boring tool at the frontlocate point in case of FIG. 5, and then, while maintaining the locatorat the same elevation relative to the ground (assuming the ground isflat), the operator walks in a direction perpendicular to thedirectional axis of the boring tool to the reference path RP, therebyestablishing a reference point 508R which is associated with the firststationary measuring location 508. With the locator in this position,the antennae 122, 124 are now generally in the y, z plane, asillustrated in FIG. 8A. In this latter regard, for purposes ofdiscussion and a frame of reference within the x,y,z coordinate system,it is being assumed that the direction of movement of the boring tool isin the x axis. This is obviously not always the case, as illustrated,for example, FIG. 5. However, in order to understand and appreciate thepresent invention, that will be assumed at least with regard to thediscussion of FIGS. 8A, 8B, and 8C. The data processing can easilycompensate for variations in the actual direction of movement.

Once the locator is at its reference point 508R corresponding with thestationary measuring location 508 of the boring tool, operator 26 letsoperator 20 know, at which time operator 20 manually actuates the remoteprocessing system 500 so that the positional information transmittedthereto from the locator, as described in conjunction with FIG. 4 isrecorded and further processed in a manner to be described hereinafter.This procedure is repeated from one location 508 to the next with theoperator most preferably following the same procedure each time, thatis, first finding the same locate point, facing in the same direction atthe locate point and then turning 90° from the directional axis of theboring tool from that locate point, consistently either to the left orto the right, and finally either moving forward or backward to thereference path to establish a corresponding reference point 508R.

As indicated previously, with the boring tool stationary at a location508 and with the locator 36′ at a corresponding reference point 508R,the two cooperate with one another so as to generate certain informationabout the position of the boring tool relative to the position of thelocator. In other words, means are provided partially at and formingpart of the boring tool and partially at and forming part of the locatorfor generating this latter information. In the case of the MercerPatents, the boring tool itself includes means for emitting thepreviously described dipole field 12 and it also includes a pitch sensorand a roll sensor. At the same time, locator 36 and locator 36′ eachincludes previously described antennae 122 and 124 and associatedprocessing components for generating the following informationcomponents:

the intensity of field 12 as measured by antenna 122 (referred tohereinafter as intensity A);

-   -   (2) the intensity of field 12 as measure by antenna 124        (hereinafter referred to as intensity B);    -   (3) the calibrated values for A and B;    -   (4) the signal ratio which is the value of one of the antennae        measurements, for example measurement A, divided by the sum of A        and B; and    -   (5) pitch.

Calibrated A and B can be accomplished in a conventional manner byinitially placing the boring tool 28 on the ground and placing thelocator a known distance from it and thereafter measuring A, B intensitycomponents and making sure that readings are adjusted to read theappropriate distances. In addition, the distance from the ground to thelocator can be compensated for as described in the Mercer Patents. Allof this information is readily available in the system described in theMercer Patent.

Referring specifically to FIGS. 8A, 8B and 8C, with this information,the depth D of the locator (FIG. 8B), the distance L between thenegative locate point used and the associated reference point 508R (FIG.8A and FIG. 8C) and the angle A (FIG. 8A) is determined by locator 36′(as it can with locator 36). Therefore, at each and every referencepoint 508R, the locator 36′ can generate information providing theposition of the boring tool at its corresponding measuring location 508and this information can be stored at or in the locator or transmittedwirelessly from the locator to the remote processing system 500 which,in turn, can record the information. As will be seen below inconjunction with FIG. 6, system 500 can then display overall path AP(based on this positional information) along with the reference path RPand it can permanently record it. In this regard, it is to be understoodthat system 500, which will be described hereinafter, can be duplicatedat the locator itself, in part or in toto, or replace the remote system,again in part or in toto. Obviously, a local system 500 would notrequire wireless receiving means. Some or all of the local system can beformed as an integral part of the locator or it can be designed to pluginto the locator as an add-on. One example of a plug-in component mightbe a lap top computer which provides the same portability as the locatoritself.

The discussion immediately above assumes a perfectly horizontally boringtool. Processing circuitry within locator 36′ and/or system 500 can bereadily provided with appropriate algorithms to compensate for pitch inthe boring tool, particularly since pitch is being directly measured andprovided to the locator. Thus, for example, if the boring tool is angleddownward 10° from it position shown in FIG. 8B, it should be clear thatthe front and rear locate points would be different. Since theprocessing circuitry in the locator or system 500 knows this from theactual measurement of the boring tool's pitch, it can compensateaccordingly.

Turning now to FIG. 6, attention is directed to the processingcomponents contained by and forming part of locator 36′ and required tointerconnect locator 36′ with remote processing system 500 in order tocarry out the method described above. These processing components (whichcorrespond to the processing circuitry of locator 36 as illustrated inFIGS. 5A and 5B in the Mercer patents) include locator processing means510 including antennae 122 and 124 for detecting field 12 and antenna126 for receiving the pitch and roll information (although a separateantenna need not be provided for this purpose). This information isprocessed so as to provide the locator operator 26 with the appropriatepositional information which can be read out by means of readoutcomponent 512 at the locator itself. This positional information istransmitted by telemetry transmitter 514 by means of radio wave to atelemetry receiver 515 and thereafter to microprocessor 516 which storesthe information selectively in, for example, an EEPROM 518. EEPROM 518could also form part of a local system 500 as discussed above and, hencecould be part of the locator itself or readily plugged into the locator.As indicated previously, only positional information that is providedduring the measurement periods described previously are stored. Thus, inthe case of processing system 500, either the remote system as shown orthe local system discussed above, the system includes an actuatablebutton 520 or other suitable means that operator 20 can actuate in orderto insure that the next incoming positional information will berecorded. Operator 26 lets operator 20 know when to actuate button 520.The microprocessor then can take all of the recorded information andgenerate a graph on display 522 and or it can input the information to apersonal computer 523 which, in turn, can provide a permanent graphicrecord which can be printed out. In this regard, if the drill pipe 10 ismeasured as it is let out into the ground, that information can be fedto the microprocessor and used in conjunction with the other positionalinformation to generate the graph.

The boring technique described above can be readily carried out by onewith ordinary skill in the art by modifying locator 36 in a way whichresults in locator 36′ and by following the procedures described herein.The modification of locator 36 resulting in 36′ is readily providable inview of the Mercer patents and the disclosure herein. Once, the boringtool 28 is guided from its starting pit, for example pit 22, to itsending or target pit, for example pit 34, the appropriate utility cableor any cable for that matter can be connected to the forward end of thedrill pipe, with or without the boring tool attached thereto, and thedrill pipe can be pulled back through the bored tunnel to the startingpit, pulling the cable with it. At the same time, it is to be understoodthat the present boring technique can be used to establish and recordthe path of the boring tool for reasons other than installing cable. Forexample, it may be desirable to record the path of an exploratorydrilling operation.

In addition to the foregoing, it is to be understood that the presentinvention is not limited to the particularly described procedure forestablishing path AP. Other procedures could be set up based on theteachings herein. For example, the procedure described calls for theoperator walking between the various locate points and the referencepath RP. Based on the teachings herein, another procedure could beestablished, for example, where operator 26 continuously walks on thereference path RP and as he or she does so the locator itself could beappropriately manipulated based on balance points and signal strengthratios in antennae 122, 124 in order to establish the actual path AP.

In the overall arrangement illustrated in FIG. 6, the processingcomponents contained by and forming part of locator 36′ and the remoteprocessing system 500 were described in conjunction with FIGS. 5, 7 and8A-C to illustrate a method of establishing and recording the actualpath taken by boring tool 28 with respect to a particular above groundreference path taken by operator 26. For purposes of the presentdiscussion, FIGS. 1 and 8B illustrate the relationship between theboring tool, actually the path it takes, and the reference pathestablished by operator 26. Note specifically that at any point on thereference path, the distance from that point to the vertically alignedpoint on the actual path is provided. Indeed, the overall arrangementillustrated in FIG. 6 is intended to provide the depth D illustrated inFIG. 8B along with the other positional dimensions shown in FIGS. 8A and8C. However, this assumes that the reference path remains unchanged.Should the terrain containing the reference path change with time, itmay be difficult, if not economically impossible, to reestablish theactual path taken by the boring tool. As will be seen below, thearrangement illustrated in FIG. 9 is designed to establish and recordthe actual path taken by the boring tool and allow the path to be easilyfound at a later date even if the terrain above the actual path changeswith time.

Turning specifically to FIG. 9, the overall arrangement shown thereincludes previously described locator 36′ and a slightly modified remoteprocessing system 500. It may be recalled that locator 36′ includes anarray of processing components including locator processing means 510for providing the positional information described previously includingspecifically pitch information, which positional information isultimately transmitted by telemetry transmitter 514 to remote processingsystem 500′. This latter system may be identical to system 500, with oneexception. System 500′ includes the microprocessor 516′ which will bedescribed hereinafter rather than the previously recited microprocessor516. Otherwise, as just stated, the two processing systems 500 and 500′can be identical. Thus, as illustrated in FIG. 9, system 500′ is shownincluding a telemetry receiver 515, an EEPROM 518, an actuatable button520, a display 522 and a personal computer 523, all of which weredescribed previously in conjunction with FIG. 6.

Microprocessor 516′ is designed to carry out all of the processing stepsof microprocessor 516 described previously and more. Specifically,microprocessor 516′ is not only able to establish the actual path takenby the boring tool with respect to the reference path taken by operator26, but it is also capable of establishing both the actual path taken bythe boring tool and the reference path with respect to a vertical surveyreference path which will not change with time. The monitor 522 and thepersonal computer with an appropriate printer serve to display in realtime and permanently record, respectively, the actual path taken by theboring tool, the reference path taken by operator 26, and the verticalsurvey reference level. All three are graphically depicted in FIG. 11.This latter figure actually represents graphically data taken duringoperation of a prototype of the overall arrangement illustrated in FIG.9, as will be discussed in more detail hereinafter.

For the moment, it suffices to point out certain aspects of thegraphical illustration. In particular, it should be noted that the graphresides in the X-Z plane, as defined previously, where the X componentof the horizontal distance traveled by the boring tool is represented bythe X axis and depth is represented by the Z axis. The vertical surveyreference level (VSRL) Is a true horizontal survey level, for example2300 feet above sea level, which is to be established by operators 20and 26 at the beginning of the boring operations. Logic dictates thatthe VSRL coincide with the starting point of the reference path taken byoperator 26, although this is not a requirement. Indeed, subsequentVSRLs can be taken to check the accuracy of the locating process. Theinitial VSRL was, however, selected in the case of FIG. 11 and is shownat VSRL in that figure. The actual path taken by operator 26 is depictedin FIG. 11 at T which actually topographically represents ground levelat the time the overall boring process was undertaken. The actual pathtaken by the boring tool is depicted in FIG. 11 at AP and alsorepresents what will be referred to as Pitch Depth with respect to thevertical survey reference level at any horizontal point along the actualpath.

Still referring to FIG. 11, at any given horizontal point on the actualpath AP, for example the point P1, the actual vertical distance betweenthat point and the reference path T is the distance D which can beestablished by either the overall arrangement of FIG. 6 or the overallarrangement of FIG. 9 as described previously. The distance between anygiven horizontal point on the actual path, for example point P1, and thevertical survey reference level VSRL is the distance which is referredto as Pitch Depth. The overall arrangement illustrated in FIG. 6 is notable to establish Pitch Depth, however the arrangement of FIG. 9 is ableto do so in the manner to be described hereinafter. By establishing andrecording the actual path AP taken by the boring tool with respect tothe vertical survey reference level VSRL, the actual path AP can alwaysbe found at a later date, even if the reference path T is lost as aresult of a change in terrain. At the same time, the overall arrangementillustrated in FIG. 9 has the additional advantage of being able tographically depict the reference path with respect to VSRL so that itsoriginal topography can be determined days, months and years latershould the terrain change.

In order to understand how the overall arrangement illustrated in FIG. 9and its microprocessor 516′ in particular establishes the actual path APtaken by the boring tool, the reference path T and VSRL, reference ismade to FIG. 10 and the data set forth in Table 1, which is providedimmediately below.

TABLE 1 Rod # Pitch Depth Pitch Depth 1 −32 23 23 2 −12 40 49 3 −1 45 574 −2 48 58 5 −9 46 65 6 −3 51 72 7 0 44 74 8 −6 44 78 9 −5 52 84 10 −554 90 11 3 53 91 12 −3 48 91 13 −3 47 95 14 −4 57 99 15 2 57 100 16 4 5097 17 0 51 94 18 −1 52 95 19 −2 49 97 20 −3 45 100 21 −7 46 106 22 −7 53114 23 0 53 118 24 2 49 117 25 −3 52 118 26 −2 45 121 27 9 41 117 28 −540 114 29 −8 47 122 30 −13 60 134 31 −5 75 145 32 4 72 146 33 4 64 141

The data in Table 1 include certain information generated by the overallarrangement of FIG. 9 as the boring tool moves through the ground. Inparticular, this information is taken at 10 foot intervals which inTable 1 are referred to as rod numbers 1, 2, 3 and so on up to rodnumber 33. The information in Table 1 includes the pitch of the boringtool at each rod number, its depth D and its Pitch Depth. The boringtool's pitch is preferably measured directly from a sensor on the boringtool, although this is not absolutely necessary. The depth D ispreferably measured in the manner described previously in conjunctionwith FIGS. 1-8. Pitch Depth is calculated in the manner to be describedimmediately below by means of system 500′ using the pitch informationfrom rod number to rod number and the fact that the boring tool moves afixed or at least a known distance from rod number to rod number, forexample 10 feet.

Turning now to FIG. 10, attention is directed to the way in which system500′ determines Pitch Depth at any particular rod number, for examplefirst at rod number 2 and then rod number 3, based on the data inTable 1. To this end, for purposes of illustration, two right trianglesare provided in FIG. 10, as indicated at T12 and T23. The right triangleT12 includes a hypotenuse A12 representing the path taken by the boringtool over a 10 foot span from rod number 1 to rod number 2, thehorizontal side B12 extending in the X direction parallel to VSRL and avertical side C12 extending in the Z direction and defining the righttriangle with side B12. An angle ∝12 is defined by the hypotenuse A12and horizontal side B12. In a similar manner, the right triangle T23includes a hypotenuse A23, a horizontal side B23, a vertical side C23and ∝23. The objective of system 500′ is to determine the length ofvertical sides C12, C23 and so on for each right triangle correspondingto each increment of movement of the boring tool. The length of each ofthese sides represents an increment of depth relative to the verticalsurvey reference level VSRL. In the case of right triangle T12, forexample, the microprocessor knows the length of hypotenuse A12 sincethis is the actual distance traveled by the boring tool from rod number1 to rod number 2. In the case of our example, this length is ten feetand can be input to the microprocessor as a given or if the overallarrangement is operating on random intervals of movement of the boringtool rather than on rod numbers, the distance traveled by the boringtool could be input by a suitable means of sensing the distance traveledby the boring tool using suitable means for sensing movement of thedrill string at the starting pit. Assuming for purposes of illustrationthat the distance A12 is 10 feet, then the only other information themicroprocessor needs in order to determine the length of side C12 andtherefore the incremental depth of the boring tool when it reaches rodnumber 2 is the angle ∝12. In accordance with the present invention, theangle ∝12 corresponds to the average pitch of the boring tool as it ismeasured at rod number 1 and rod number 2. In Table 1, the pitch of theboring tool, as directly measured, is −32 percent grade, where the minussign indicates that the pitch angle is downward and to the right, asviewed in FIG. 10. The pitch of the boring tool, as measured at rodnumber 2 is −12 percent grade. Microprocessor 516′ uses this informationto establish an average pitch which is −22 percent grade based on thefigures provided. At some convenient point in this calculation process,the microprocessor converts the average pitch angle of ∝12 from percentgrade to degrees. Thus, −22 percent grade converts approximately to −12degrees. Thus, with ∝ being −12 degrees and the hypotenuse being 10 feetor 120 inches, vertical side C12 can be readily calculated by themicroprocessor according to the equation Sin ∝=C12/A12. The only unknownin this equation is C12. In the case of our example, the length of C12is approximately 26 inches. Therefore, Δ Pitch Depth is approximately 26inches and the total Pitch Depth from VSRL to the rod number 2 point is49 inches.

Turning now to triangle T23, the microprocessing steps just describedare carried out to determine the length of side C23, that is, Δ PitchDepth from rod number 2 to rod number 3. In this case, the actual pitchof the boring tool at point 2 is measured at −12 percent grade, theactual pitch of the boring tool at point 3 is measured at −1 percentgrade, thereby resulting in an average pitch of −6.5 percent grade.This, in turn, converts to approximately −3.7 degrees. The hypotenuseA23 is known to be 10 feet or 120 inches. Therefore, the incrementallength C23 or Δ Pitch Depth is approximately 8 inches and, therefore,the overall Pitch Depth at rod number 3 is 57 inches.

In Table 1, the Pitch Depth distance from VSRL at each and every rodnumber from rod number 1 through rod number 33 is shown and was measuredin the matter just described. These data are graphically reproduced inFIG. 11 where it can be seen that each point on actual path AP taken bythe boring tool is located at a Pitch Depth distance below VSRL withactual measurements being taken every 10 feet and interpolations beingmade therebetween. For example, the graph clearly shows that at 16 rodlengths out (160 feet) the boring tool is 97 inches (Pitch Depth) belowVSRL. This is true whether or not the reference path taken by theoperator at the time the information is gathered or is available.

It should be noted that establishing and graphically recording actualpath AP with respect to VSRL does not require the depth D informationthat both arrangements of FIG. 6 and FIG. 9 can provide. However, itshould also be noted that the depth D information is part of the data ofTable 1. It is provided so that the reference path which is labeled T inFIG. 11 and RP in FIGS. 5 and 10 can be graphically depicted relative toVSRL and the actual path AP. In this way, if the terrain does not changeas time goes on, the actual path T can be used to find the path taken bythe boring tool. On the other hand, if the terrain does change, thevertical survey reference level can be used to find the actual pathtaken by the boring tool. Also, if for any reason the terrain changesand it is desired later to know what the terrain looked like when theboring process took place, such information is available from the curvesof FIG. 11. With particular regard to VSRL, as stated previously,subsequent VSRLs can be taken and compared with calculated Pitch Depthdata to test the accuracy or provide corrections to the calculationsbased upon the boring tool Pitch Data.

Two embodiments of the present invention have been describes thus far.The first embodiment related to an overall process for establishing thepath taken by a boring tool with reference to the path taken by operator26 as the operator carried locator 36′. This embodiment was describedherein in conjunction with FIGS. 1-8 which included a description of thelocator 36′ and system 500 illustrated in FIG. 6. The second embodimentadded to the first embodiment the ability to establish the path taken bythe boring tool not only in conjunction with the reference path taken byoperator 26 but also with respect to the vertical survey referencelevel. This second embodiment was described herein in conjunction withFIGS. 1-8 in combination with FIGS. 9-11 including, in particular, FIG.9 which illustrated a modified system 500′ along with the previouslydescribed locator 36′. As will be described in more detail hereinafter,the preferred way in which each of these latter embodiments is practicedis illustrated in FIGS. 12-15.

Turning specifically to FIGS. 12 and 13, a more definitive illustrationof the positional relationship between boring tool 28 and ground level(the reference path T taken by operator 26) is shown. In particular,FIG. 12 specifically illustrates the pitch angle ∝ of the boring tool(actually its transmitter), the depth of the boring tool and one of thepreviously recited negative locate points, as well as Radial Distancefrom the boring tool to that negative locate point and the ForwardDistance f. FIG. 13 specifically illustrates the angle Φ correspondingto the angle of the flux plane from the boring tool to the ReferencePath and the offset distance Σ. These variously positional andorientational values are used in a manner to be described.

FIG. 14 diagrammatically illustrates in block diagram form themicroprocessing that takes place in locator 36′ in accordance with apreferred version of both of the previously described first and secondembodiments of the present invention. Note specifically that FIG. 14actually illustrates the microprocessor and the locator including itsinputs and its outputs. The inputs shown in FIG. 14 include the signalstrength of the previously recited antenna A, the signal strength ofpreviously recited antenna B, and coded data (digital data)corresponding to the role and pitch of boring device 28, its batterystatus, its temperature as well as other possible information that canbe provided in digital, coded data form. The microprocessor in responseto these inputs delivers at its output what is referred to as a datagroup A comprised of magnetic range (the distance between the locatorand the boring tool or some other parameter related to the totalmagnetic field strength and the calibration factor), signal strengthratio (the signal strength of A divided the sum of the signal strengthsof A+B), the vector sum signal strength (the square root of A²+B²), andthe digitized coded data which is passed through from the input of themicroprocessor.

Turning to FIG. 15, this figure illustrates a modified version 500″ ofsystem 500′ but provides the same function, as described previously inconjunction with system 500′. System 500″ includes a remote display 530,that is remote with respect to the locator 36′ and a microprocessor 532within the remote display. System 500″ also includes a data loggermodule 534. This module includes its own microprocessor 536, a keypad538, memory (E²PROM) 540, a clock 542 and provision for connection to apersonal computer 544 (see FIG. 16) such as a laptop computer. Theremote display 530 and the data logger module 534 are typicallypositioned at the starting pit with operator 20.

Still referring to FIG. 15, as shown there, the data group A istransmitted by means of telemetry from the output of the microprocessorof locator 36′ to the input of microprocessor 532. In this way, theremote display is able to display everything the locator displays buthas the ability to do it in at least partially a different format.Specifically, the locator does not display the signal strength ratio butthe remote display displays the ratio as a left/right steeringindication. The locator displays signal strength but the remote displaydoes not. In addition, the microprocessor 532 outputs the previouslydescribed magnetic range, signal strength ratio and coded data to theinput of microprocessor 536 in the data logger module. Using keypad 538,operator 20 at the starting pit is able to store this information intomemory 540 at desired points in time, for example at ten feet incrementsof forward movement of the boring device. In this regard, using thekeypad, operator 20 can vary the time in which data is stored and, infact, can modify the storage of data. For example, should it benecessary to pull the boring tool rearwardly in order to, for example,pass around an obstruction, it may be necessary for the operator tostore new data corresponding to the positions the boring tool are causedto pass through again as a result of the backtracking. Clock 542 can beused to time and date stamp the data as it is stored to recover thelatest data as a result of the backtracking. The present inventionfurther contemplates providing data logging within remote locator 36′.That is the logged data is stored within the remote locator itself,rather than being transmitted by telemetry to another location. In thisinstance, a “log” button (not shown) is provided on locator 36′ suchthat data is logged in response to the operator of the remote locatordepressing the log button. The logged data could be stored, for example,in EEPROM. It should be appreciated that by placing such data loggingfunctionality into the remote locator, communication between the remotelocator operator and the drill rig operator would not be required fordata logging purposes.

Referring now to FIG. 16, attention is directed to a dipole equationsolver 546 which is software in personal computer 544. As seen in thislatter figure, the dipole equation solver is adapted to receive thepitch ∝ of the boring tool, magnetic range and signal strength ratioeither at the time of drilling or recalled later from the data logger.The dipole equation solver is configured to compute Depth D, ForwardDistance f, offset Σ and angle Φ. In addition, the dipole equationsolver of the present invention is configured for computing the depth ofthe boring tool beneath the surface of the ground when locator 500″ ispositioned at a forward locate point (see FIG. 2) or reference point508R (see FIG. 5), as will be described in further detail immediatelyhereinafter.

Continuing to refer to FIG. 16, the present invention recognizes thatthe depth of the boring tool beneath the surface of the ground or anyother reference surface is related to the signal strength of locatingsignal 12 at a forward locate point or reference point, to the pitch ∝of the boring tool at that forward locate or reference point and to thesignal strength ratio of antennas 122 and 124 (see FIG. 3). Havingdisclosed the existence of this relationship, one of ordinary skill inthe art may approximate the relationship, for example, by a cubic curvein a way which permits dipole equation solver 546 to rapidly determinethe depth of the boring tool with a relatively high degree of accuracyusing minimal computing capacity. It is noted that one of ordinary skillin the art may appropriately adjust the equation or use the exactequations in view of the need for higher accuracy or due to theavailability of higher processing power. Moreover, other parametersincluding forward distance (f), offset (Σ) and the angle of the fluxplane may be solved for with the locator at the forward locate point orreference point. Any of these parameters may be displayed, if sodesired. As just one example, offset (Σ) may be used to generate asteering display (not shown) which graphically shows the operator howfar left or right of the desired path the boring tool is located or,conversely, how far left or right the boring tool (i.e., locating signaltransmitter) is relative to locator 36′. It is to be understood that thepresent invention contemplates the use of any negative locate pointwithin the context of these teachings. Therefore, rear locate points maybe used, however the description above has been limited to a forwardlocate point and associated reference point or points for purposes ofsimplicity.

Turning to FIG. 17, in accordance with the present invention, theforward distance, f, may be used in conjunction with pitch, φ, in ahighly advantageous manner for predicting the depth of a boring tool 600during drilling beneath the surface of the ground 601. Morespecifically, the depth D′ of the boring tool may be predicted at aninground forward point 602 which corresponds to and lies verticallybelow the front locate point (FLP) at the surface of the ground. It isto be understood that the front locate point comprises a point, among apossible number of points including the rear locate point, which isdefined by the locating field transmitted from the boring tool and thatestablishing the location of the front locate point is in no way coupledwith a specific embodiment of a locating tool or instrument. Hence, thefront locate point may be referred to in the remainder of thisdisclosure and in the appended claims as a field defined forward point.

Continuing to refer to FIG. 17, boring tool 600 is illustrated travelingalong a predicted path 604 from an inground upstream point 606 in adirection indicated by an arrow 608 toward the inground forward point.Path 604 is assumed to be straight and proceeds at the pitch, φ, whichis the pitch of the boring tool at inground upstream point 606. Asdescribed above, φ may be obtained as data measured by a pitch sensorhoused within the boring tool, while forward distance, f, may becalculated based on φ and the strength of the locating signal.Thereafter, an increment I may determined as (f*tan φ). Depth D,corresponding to the inground upstream point, may also be calculatedusing the calibrated magnetic locating signal intensity, the height of alocating receiver above the ground and φ. Depending on whether φ ispositive or negative, increment I is appropriately added to orsubtracted from D in order to calculate predicted depth D′. In thepresent example, I is subtracted from D in arriving at the proper valuefor D′. The latter may then be displayed on the locator unit and/ortransmitted by telemetry to a location such as, for example, the drillrig. It is noted that, in this particular example, the boring tool is ata depth which is less than D at inground upstream point 606 due to thetopography of the surface of the ground. Nevertheless, the determinationof D′ beneath the surface of the ground at the field defined forwardpoint is correctly predicted.

Still referring to FIG. 17, it should be appreciated that the predicteddepth feature of the present invention is highly advantageous since theoperator of the system may make appropriate steering adjustments in theevent that the predicted depth is inappropriate. For example, theoperator may be standing above an obstacle at a known depth. In thismanner, the operator can ensure that the boring tool passes either aboveor below the obstacle with a greatly reduced risk of hitting it. Inaddition, the time consuming process of drilling to the obstacle,realizing that the tool is about to hit the obstacle, retracting theboring tool and then re-drilling is avoided. It should be noted thatdistance f depends on depth D along with φ, and that f may be farenough, within the steering capabilities of a typical boring tool, thatan appropriate course correction may readily be performed.Alternatively, at less depth when f decreases, constraints imposed bythe steering capabilities of the boring tool may necessitate pulling theboring tool back an appropriate distance such that course correction maybe accomplished prior to the boring tool arriving at forward point 602.As an additional note, the present invention contemplates any suitablemethod for determining predicted depth D′. For example, D′ may readilybe approximated by a cubic curve in lieu of the full dipole equations orapproximated by a calibration curve. One of ordinary skill in the artmay derive the equations relating D′ to the calibrated signal strengthand the pitch using known dipole equations. It is submitted that thedepth prediction feature of the present invention has not been seenheretofore and remarkably enhances the capabilities of any drillingsystem into which it is incorporated.

The above procedure was described based on the orthogonal arrangementshown in FIG. 5. However, other antenna arrangements could be employedso long as they provide a known relationship to the locating field. Forexample, a single vertical antenna in combination with the pitch of theboring tool may be used to obtain a predicted depth at a field definedforward point since the magnetic field is vertical at this point.

In the above discussion, dipole equation solver 546 was assumed to beimplemented within locator 36′, but remote processing could also beemployed and the results displayed remotely and/or telemetered back tothe locator for display.

All of the previously described arrangements assumed that the locatormade its measurements at ground level which is of course possible.However in one preferred embodiment, operator 26 holds the locator at acomfortable position above ground, as shown in FIG. 1. In this case, thelocator includes an ultrasonic measuring mechanism indicated by theinput U/S in FIG. 6, as described in prior Mercer patents (cited herein)to compensate for the differences between the locator and ground level.In a second embodiment, the operator maintains the locator at a fixedline such as one produced by a laser. In this case, the locator itselfincludes a target spot which the operator can line up with a given laserbeam defining the particular line. At the same time, the previouslymentioned measuring mechanism can be used to measure to ground level. Itshould be appreciated that in any embodiment which compensates for thelocator being held significantly above the surface of the ground, thelocator may readily compensate for predicted depth at the field definedforward point in view of the height of the locator above the ground. Forexample, in one technique, the field defined forward point is identifiedusing a locator which is held at a distance above the surface of theground. The distance between the field defined forward point and thesurface of the ground may be measured using, for example, the disclosedultrasonic measuring mechanism. Thereafter, the measured distance of thelocator (i.e., the field defined forward point) above the ground may beused in predicting the depth of the boring tool beneath the surface ofthe ground.

It should be appreciated that the concepts of the present invention, asused in the method taught herein, may be applied in a number ofdifferent ways by one of skill in the art. Therefore, the presentexamples and methods are considered as illustrative and not restrictive,and the invention is not to be limited to the details given herein, butmay be modified within the scope of the appended claims.

1. An apparatus for use in a system including a steerable boring toolwhich transmits a dipole locating signal and for avoiding an ingroundobstacle at a known depth, and said boring tool is configured fortransmitting a pitch orientation signal, said apparatus comprising: asignal strength detector for measuring a signal strength of saidlocating signal at a location above the inground obstacle serving as afield defined forward point of the locating signal and with the boringtool located at a first position that is a forward distance from theobstacle such that the signal strength is representative of the depth ofthe boring tool at said forward distance from the obstacle; a pitchsensing arrangement for determining a pitch orientation of the boringtool using the pitch orientation signal; and a processor for determininga predicted depth of the boring tool, based on at least generallystraight movement of the boring tool by said forward distance toward theinground obstacle, said signal strength and said pitch orientation foruse in steering the boring tool in a way that is intended to avoid theobstacle based on the predicted depth of the boring tool and the knowndepth of the obstacle.
 2. The apparatus of claim 1 wherein said boringtool is characterized by a set of steering capabilities and saidprocessor is configured for comparing said forward distance with saidsteering capabilities to determine a course correction for the boringtool to cause the boring tool to miss the obstacle.
 3. The apparatus ofclaim 2 wherein said processor is configured for establishing thatsteering the boring tool forward from said first position, based on saidsteering capabilities and using said course correction, provides agreatly reduced risk of hitting the obstacle.
 4. The apparatus of claim2 wherein said processor is configured for establishing that steeringthe boring tool forward from said first position, based on said steeringcapabilities, is insufficient to provide a greatly reduced risk ofhitting the obstacle.
 5. The apparatus of claim 1 configured for usingsaid field defined forward point substantially located on the surface ofthe ground.
 6. The apparatus of claim 1 configured for establishing saidfield defined forward point at a height above the surface of the groundand for determining a distance between the field defined forward pointand the surface of the ground and said processing arrangement, forpredicting the depth of the boring tool below said field defined forwardpoint, is configured for determining the predicted depth, based on theheight between the field defined forward point and the surface of theground, in conjunction with the measured signal strength and the pitchorientation.
 7. The apparatus of claim 1 wherein said processor isconfigured for predicting said depth by (i) using said forward distanceas a horizontal distance between the field defined forward point andsaid boring tool, (ii) determining the depth of the boring tool at saidforward distance from the obstacle and (iii) using the depth of theboring tool at said first position and the pitch orientation,determining a predicted depth change increment below said field definedforward point.
 8. The apparatus of claim 7 wherein said predicted depthis determined as the depth of the boring tool at said first positionplus or minus said predicted depth change increment.
 9. The apparatus ofclaim 7 wherein said processor is configured for determining saidpredicted depth change increment as being equal to the tangent of thepitch orientation, as determined at said first position multiplied bysaid forward distance.
 10. The apparatus of claim 1 further comprising:a display for displaying said predicted depth.
 11. The apparatus ofclaim 1 wherein said processor is configured for using the pitchorientation and signal strength in a way which directly determines thepredicted depth.
 12. The apparatus of claim 11 wherein said processordetermines the predicted depth using a cubic curve function.
 13. Theapparatus of claim 11 wherein said processor determines the predicteddepth using a calibration curve.